Process and apparatus for the manufacture of cellulose



April 18, 1933. D. NESTA'D 1,904,394

PROCESS AND APPARA'Tus F011 'rms umunc'ruma 0F cELLpLosE Filed A ril 4,1951 z Sh m-sheet 1' D. WESTAD April 18, 1933.

PROCESS AND APPARATUS FOR THE IANUFAC'I'URE QF CELLULOSE z Sheets-Sheet 2 Filed A in 4, 1931 April 18, 1933. D. WESTAD 4, 9

- PROCESS AND APPARATUS FOR THE unumc'runm OF CELLULOSE Filed April 4. 1931 s sneets sneet a Patented Apr- TS, 1933 UNITED STATES \P'ATENT "orrlca naimzr. wns'ran, or BYGDOY NEAR osno, roman! PROCESS AND APIB AB ATUS FOR. THE MAl IUFACTU BE 6F GELLUIOBI Application fled April 4, 1931, Serial 110.5273, and in Norway Kay 87,

, This invention'relates to the manufacture of cellulose by heating wood chips or other cellulosic materials under pressure with aqueous solutions of chemicals capable of dissolving the incrustations of the raw material, thus liberatim the cellulose fibres,- and the invention has For its object a method of carrying this process into effect, which allows of obtaining an increased yield of cellulose of 10 first class quality as compared with the processes hitherto employed.

It is a well ,known fact that the output of cellulose obtainedunder the present practice do not by far correspond to the percentage of cellulose fibres contained in the raw materials (wood straw etc.), aconsiderable proportion of the fibres being! in fact lost during.

the digestion operation. This loss is to a greatextent due to the fact that the raw material is subjected .to a very uneven attack of the dissolving chemicals, so that the fibres first liberated will become destroyed before the remainder of the charge has been sufficiently acted upon,

According to the present invention these drawbacks are avoided by combining the digestion operation at elevated temperatures with a preparatory treatment of the wood chips or other cellulosic raw materialwith digestion liquor at'low temperatures, but under high pressure.

Th's method of siderable shortening of the time, in which the material is subjected to high temperatures and thus also an important decrease in the consumption'of steam, at the same time as an increased output of first class cellulose is obtained. 1

The digestion operation and the preparatory treatment with digestion liquor at low temperaturesunder high pressure may be carried out in the same vessel, viz. an ordinary digestor, but it is preferred to carry the operations into effect as separate steps in two or more separate sets ofcontainers, so arran ed in relation to one another that the material (wood chips and the like) can be readily transferred from one set of containers to another.

As will be'underst'ood, the process accordoperation allows of a coning to the invention is composed of two main phases: the impregnation base and the digestion or cooking phase. l uring the impregnation stage, the cellulosic material (wood chips andthe like) is subjected to the action of digestion liquor under'a high pressure, but at a relatively low temperature (viz. below 100911., usually between and 15; C. and even down to near zero).

Prior to the impregnation with digestion 6 liquid when employed as a ste in such digestion process which is carrie out by. the use of sulphite solutions or other solutions prepared by the use of gaseous reaction componentsmay go a treatment of the chips 5 with the gaseous reagent or reagents. This treatment with gaseous reagents may also suitably be efl'ected at low temperatures and in the same container as that in which the subsequent impregnation with liquid under 70 pressure takes place. The gas may be applied under ordinary or increased pressure and even under pressures sufliciently high to bring about partial or complete condensation of the gas. r

When the invention is applied to the sodaor sulphate-process or to other processes, in

which gaseous reaction components are ordinarily not made use of, the reparatory treatment which is referred to a ove, will be omitted, although it may under certain circumstances be considered desirable from particular reasons to combine even these types of processes with a preparatory treatment with some gaseous reagent.

In the preferred embodiment of the invention, the impregnation step and the di estion step are carried out in diflerent vesse s, and v these vessels are suitably arranged above one another. Thus the impregnation vessel may be arranged on the floor above the digestors, so that the mixture of impregnated chi s and impregnation liquid can be transferre to the digestor under the actionof its ownweight. The transfer of the charge is facilitated by 9 giving to the containers a form, adapted for the purpose. The form of the vessel is suitably so elected as to romote as far as possible the utilization of t e gravity of the charge to convert same into a cyclonic centripetal moin relation to this container walls.

tion. It is suitable for the purpose inquestion to use containers, having tapering side walls, so that the sectional areas increase towards the bottom of the container. It is also suitable to arrange the discharge openin so that its center lies outside of a vertical line through the center of gravity of the char. e.

A suitable container may for example considered as composed of a conical main ort1on and a non-symmetrically cup-shaped ttom rtion,havingadeepened art, in which the ischarge o ning is placecfeccenlgricall x r1- ence has roved that a vessel so constrliifted can re I be em tied of a charge consisting of wood 0 ips and liquid. I a In order to promote the discharge of the material, it may also be of advantage to provide the bottom portion of the container around the discharge opening with recesses, ribs or vanes, so arranged as to form an an le with radial lines throu h the center of t e discharge opening.v Ot erwise any type of container may be used forthe. reparatory treatment of the chips, provided tihat the allow of rapid and complete emptyingo the contents. The vanes or ribs referred to above may with advantage be used in containers of any type and in combination with excentrically as well as with centrallyarrangod discharge openings. It is no necessary condition I -sectiononline-IV-IV of Fig. 2, an

that the vanes are arranged immediately adjacent to the outlet or at the bottom of the container. The desired effect will be pro-- duced also when the vanes are arranged on or nearto the side walls of the container.

When containers without guide ribs or vanes, or containers with centrall arranged discharge outlet are made use of, it will usually be necessary to arr very large outlet channels or to make use 0% moving emptyingmembers or agitators of one kind or another.

A plane for carrying the invention intoef feet may'for example consist of two spherical digestors of 2i) m capacity each one preheating container of 32 in capacit above said digestors and two interim ta (impre nation containers) with a capacity of eac 46 m, arranged above the said preheating containers. I

A plant of this type is diagrammatically I illustrated in the accompanying drawings in which 1 is a diagrammatic representation of the P w a Fig. 2 1s a vertical sectional view, on an enlarged scale, of one of the impregnation Fig. 8 is a horizontal sectional view of the same tank on lines III-III of F 2 Fig. 4 is a side view of the ta partly in I his a horizontal sectional view of an im regnati 'on guide members on tbe bottom. I

1 and 2 represent the impre ation tanks, 3 the preheating (or precooking container and 4 and 5 the digestors.

When cellulose is to be manufactured from wood chips according to the 'sulphite process by the use of the illustrated plant, one may for example operate as follows: 7

The interim tanks (impregnation tanks) 1 and 2 are charged with chips, containing for example 32 per cent of moisture. This moisture percentage may be the result of a preceding soaking of the chips, in water orsome aqueous solution of chemicals, or it may be the original moisture of the wood, from which the chips have been cut.

tank 1 through an inlet at the bottom. The gas displaces the air contained in the charge of chips and is absorbed inthe water contained in the chips. When the chips have impregnation vessel, iit may be found desir-' able, when the ve'ssel has been charged with liquid, to maintain the liquid in circulation for a short period oftime, for example by means of a pump inserted in a pipe line, connecting thetop and bottom parts of the impre ation vessel.

e tank is thereupon laced under a pres- Sulphur dioxide gas is now introduced into sure of about 6 atmosp eres by liquid (or gas) ressure, while the temperature is maintaine below 70 C., for example at about 20 After about 6 hours, the presure is relieved and the mixture of chips and li uid is run into the preheating vessel'3. E cient mixing of chips and liquor is promoted by the cyclonic motion oft e charge during the transfer to the preheating vessel, and may be further promoted by pumping liqluor from the bottom of the preheatingvesse into the interim tank at a int above the charge.

The temperature in the charge thus introduced into the preheatin vessel is now for exam le about 20 0. he charge is then hea to boiling temperature. After about 3 hours, the char is introduced into one of the di tors. e transfer and the mixing of chi and liquor is romoted by clrculatlon of 'quor as descri d in connection with the transfer from interim tank to pre- I heating vessel.

The digestion operation is carried out in process is terminated and the digestors em tied.

n the meantime, a new charge of chips has been prepared in the interim tank 2 and preheater 3 and run into the second digestor 5. The impregnation of this second charge in interim tank 2 takes place during the same period of time as that, in which the first prepared charge is under treatment in digestor 4.

The operation of the plant is thereupon continued in the same way by the constant use of the interim tanks and the preheating vessel to prepare new charges for introduction into the di estors. 1

All steps or pisses of the process thus take place synchronously, and in these synchronous operations, the process difiers' fundamental! from what takes place when the various p ases all take place in one and the same vessel as is the case in known processes for the manufacture of cellulose.

The above described method of operation is onl to be considered as an example, in

that t e various details in the recess itself as well as in the apparatus emp oyed may be varied within wide limits and modified according to circumstances, for example so as to make it possible without reducing the capacity of the plant to produce at choice diferent qualities of pulp, requiring a short: ened or extended digestion period.

When operating as above described, any other type of digestion liquid than calcium of course be employed, such as for examp e sulphite solution, in which the base is magnesia, potash, soda or am- ,monia or mixtures of two or more of these bases, with or without auxiliary additlons,

such as for example salts of strong acids etc. The employed bases or auxiliary additions may also be added in part to the digestion liquor, before it is brought into the impregnation vessel; but they may also be used at least in part to prepare the chips or other celluloslc raw materialfpreviously to the introduction of the sulphurous acid gas into the charge.

As regards the employed digestors, these.

may be of any known or suitable type.

It will be understood that the'process as described maybe carried outalso without the use of special preheatin vessels 3. In this 5 case the charge is direct y trarsferred from the, impregnation tanks 1, 2 to the digestors 4, 5. The number of digestors will then havev to be increased with one for each two impregnation tanks. The volumes of the di estors will then have to be dimensioned as or the preheating vessel in the described example.

' The invention is not limited to the use of two or three sets of containers, but covers the execution of the process in any number of stages carried into efiect in succession in separate containers,

same

because in fact the utilizachips have to pass.- With the increase in number of vessels operating in series will follow also an increase in the homogeneity or uniformity of the resulting cellulose pulp as well as in the yield calculated on the employed raw material.

I claim:

1. A process of recovering cellulose from raw materials, comprising subjecting a charge of the raw material to impregnation with a digestion-liquid under a pressure raised several atmospheres above normal and at a temperature considerably below 100 C. in a closed impregnation vessel for a period of several hours, thereupon transferring the entire charge including the contained digestion liquid into another vessel, and then heating the charge consistingof im regnated raw material and digestion liqui to digestion temperatures considerably-above 100 C. for a period of time sufficient to effect complete dissolution of the incrustations on the material.

of material, impregnating same with a digestion-liquid in one container, and thereupon transferring the charge into another container for continued treatment with digestion liquid, said digestion liquid being circulated from the container receiving the charge into and through the container from which material is being discharged, the said circulation being continued for a sufliciently long period of time to obtain a liquid of uni- "form composition in the receiving container.

4. A process for the recovering of cellulose from raw materials, comprising subjecting a batch of the raw material to impregnation with digestion 1i uid in an impregnation chamber for a de nite period of time, subjectingi another batch of the material to the ind of impregnation in another impregnation chamber for the same period of time as that of the first named batch, trans-' ferring the first named batch in its entirety, from the impregnation chamber into a secondary treating chamber and retaining same in this chamber for a definite period of time, removing the treated charge from said secondary treating chamber, and immediately afterwards transferring the second impregnated batch in its entirety directly from the second impregnationv chamber into the secondary treating chamber and retaining same therein for the same period of time as the removed batch.

5. A container for'impregnating cellulosei downwardly m 6. A container for impregnating cellulose ment'thereof, in another container, the con-- materials with aqueous solutions of chemicals rior to digestion-treatment thereof 1n anotiier container, the bottom of said container having the form of a trou h sloping towards a oint near the wall 0 the container a dlscharge outlet for impregnated material being arranged at said polnt, and a irected discharge tube.

materials with aqueous solutions of chemicals as a separate step prior to digestion-treattainer having an overhanging Wall and the bottom of the container having aneccentrical- 1y arranged discharge openin overhanging container-walLsai opening being located at a point towards which the bottom slopes from all sides. I

7. A container according to claim 5, in which there is provided interior guide members so arranged in relation to the flow of the charge during discharge through the opening in the bottom that they effect a whirling motion of the charge around a vertical ans.

8. A multiple-stage process for recovering cellulose from raw materials in which a charge of the material is impregnated with reactive liquid in one container and is subjected to a final digestion treatment in another container, the duration of the impregnation treatment in relation to the duration of the digestion treatment being shortened or lengthened by decreasing or increasing respectively the number of impregnation containers in cooperative operation with the digestion containers.

9. Process of recovering cellulose from raw materials comprising subjecting a charge of the raw material to the action of gaseous sulphurous acid so as to effect absorption of gaseous sulphurous acid in the moisture in the interior of the lndividualpiecesof raw material, thereupon subjecting the so. re-

pared charge to im regnation with sul it/e digestion liquid un er a pressure raise-(1 several atmospheres above normal and at a temperature considerably below C. in a closed impregnation vessel for a period of several hours, and thereafter heating the char e consisting of impregnated raw materia and acid sulphite digestion liquor to digestion temperatures considerably above 100 C. for a period of time suficient to at fect dissolution of the incrustations of the material.

In testimony whereof I have signed name unto this specification.

.' DANIEL WFlSTAD.

- near said- 

